1. Field of the Invention
This invention relates to a piston ring for internal combustion engines, and more particularly to a piston ring whose piston ring sliding surface is provided with a channel having a chrome plating layer (hereinafter referred merely to as a "chrome insert piston ring").
2. Description of the Prior Art
Conventionally, a chrome insert piston ring which is provided in its sliding surface with a cast iron base body 1' and a chrome layer 4 as illustrated in FIG. 1 of the drawings has been used in order to improve its early fit during the breakingin period after the piston ring has been incorporated and also to improve its wear resistance during normal or steady operation.
The prior art chrome insert piston ring of this type, however, does not have sufficient scuffing resistance. That is, since the hardness of the chrome layer 4 and that of the cast iron base body 1' of the piston ring sliding surface are different during operation a small difference (.alpha.) in level will appear therebetween as illustrated in FIG. 2 so as to form projecting sharp edges 4' and 4" which will come into contact with the mating cylinder wall, resulting in scuffing occurring, particularly when lubrication is poor. Also, oil-up tends to occur with the prior art chrome insert piston ring since the upper edge of the upper land 1' and the lower edge of the lower land 1' of the piston ring usually both must be bevelled to a large degree in order to prevent scuffing as much as possible. If the beveling is small, scuffing would readily occur. In addition, recently engines have been designed to have higher power, pressure level and speed, and thus the piston ring for these engines naturally must have a sliding surface with higher wear resistance and with higher scuffing resistance in accordance with the tendency.